There have recently been increasing demands that substrates formed of organic materials such as plastics and inorganic materials such as glass be improved in terms of antifogging properties and antifouling properties.
As an approach to solving the fogging problems, a method has been proposed in which an antifogging coating containing a reactive surfactant and an acrylic oligomer provides enhanced hydrophilicity and water absorption (see, for example, Non Patent Literature 1). The fouling problems have been addressed by methods in which the hydrophilicity of the surface of materials is enhanced so that fouling such as hydrophobic substances in the air which have become attached to surfaces such as exterior walls can be detached and removed from the surface by water spray or rainfall (see, for example, Non Patent Literatures 2 and 3).
As proposed in the art, the use of hydrophilic materials such as hydrophilic resins is a possible remedy to solving the problems related to fogging, fouling and the like. Many resins having a large number of hydroxyl groups in the molecule, for example, polyvinyl alcohols are known as the hydrophilic resins.
Other hydrophilic resins which are known are, for example, resins obtained by polymerizing 3-sulfopropyl methacrylate potassium salt, 2-acrylamido-2-methylpropane-sulfonic acid sodium salt and polyethylene glycol diacrylate (see, for example, Patent Literature 1), resins obtained by polymerizing 3-sulfopropyl methacrylate sodium salt and long-chain urethane diacrylate (see, for example, Patent Literature 2), resins obtained by polymerizing 2-sulfoethyl acrylate, tetrahydrofurfuryl acrylate, trimethylolpropane acrylate and spiroglycol urethane diacrylate (see, for example, Patent Literature 3), resins obtained from 2-sulfoethyl methacrylate and/or phosphoric group-containing (meth)acrylate, and epoxy resin (see, for example, Patent Literature 4), and resins obtained by polymerizing hydroxyethyl methacrylate, sulfoalkylene (C6 to C10) methacrylate and methylenebisacrylamide (see, for example, Non Patent Literature 4).
The hydrophilic resins of Patent Literature 1 are in the form of transparent gels and are allegedly usable as bioadhesives. The hydrophilic resins of Patent Literature 2 are described to be excellent in ink absorption, have high water resistance and be usable as blocking-free recording media in inkjet recording systems. Patent Literature 3 describes that the hydrophilic resins can strongly bond a metal hub for the driving of optical information disks with a resin substrate. The hydrophilic resins of Patent Literature 4 are allegedly usable as conductive cured films exhibiting excellent mechanical performance, solvent resistance, film-forming properties, adhesion, transparency and abrasion resistance. Non Patent Literature 4 discloses that the hydrophilicity of a lightly crosslinked film of the hydrophilic resin formed on glass varies depending on the length of the alkylene chain (C6 to C10) of the sulfoalkylene methacrylate used as a monomer (advancing contact angle and receding contact angle) as well as depending on the hydration time.
However, most of the above hydrophilic resins have a relatively low degree of intermolecular crosslinking to exhibit high water solubility or to show, if not being water soluble, a tendency of absorbing water to forma gel. Further, the surface is soft and easily scratched in some cases due to the relatively low degree of intermolecular crosslinking.
Further, some of the above hydrophilic resins are insufficient in terms of hydrophilicity and cannot perform appropriately as antifogging materials and antifouling materials.
On the other hand, Patent Literature 5 proposes a hydrophilic material which has a bilayer structure produced by double coating, first by applying a crosslinkable polymerizable monomer composition onto the surface of a substrate and incompletely polymerizing the composition while controlling the dose of UV irradiation to form a crosslinked polymer, and subsequently applying a hydrophilic monomer and performing UV irradiation again to block- or graft-polymerize the hydrophilic monomer to the surface of the crosslinked polymer.
However, this double coating process is complicated, adds costs, and is often unsatisfactory in terms of surface smoothness compared to a usual single coating process for producing a monolayer structure.
The present inventors have proposed a polymer obtained from a hydroxyl group-containing (meth)acrylamide as an approach to solving the above problem (see Patent Literature 6).
However, the properties of the polymer are still to be improved for the polymer to be used as an antifouling film or an antifogging film.
Further, the present inventors have proposed another approach to solving the above problem wherein a monolayer film has specific anionic hydrophilic groups present in a high concentration on the surface (see Patent Literature 7).
However, the properties of the film are still to be improved for the film to be used as an antifouling film or an antifogging film.